Figure 1.

Characterization of the polyethyleneimine (PEI)-coated Fe₃O₄ NPs. (A) The transmission electron microscope (TEM) image of the Fe₃O₄ NPs without PEI. Scale bar indicates 50 nm; (B) the particle size distribution of the Fe₃O₄ NPs without PEI, from the analysis of TEM images; (C) the TEM image of the PEI-coated Fe₃O₄ NPs. Scale bar indicates 50 nm; (D) the particle size distribution of the PEI-coated Fe₃O₄ NPs, from the analysis of TEM images; (E) the hydrodynamic size of the Fe₃O₄ NPs without PEI, analyzed by dynamic light scattering (DLS). (F) the hydrodynamic size of the PEI-coated Fe₃O₄ NPs, analyzed by DLS; (G) The magnetization curve of the Fe₃O₄ NPs without PEI was analyzed by magnetization curve obtained by vibrating sample magnetometer (VSM) at room temperature; (H) The magnetization curve of the PEI-coated Fe₃O₄ NPs was analyzed by magnetization curve obtained by vibrating sample magnetometer (VSM) at room temperature; (I) the thermogravimetric analysis curve of the Fe₃O₄ NPs without PEI; (J) the thermogravimetric analysis curve of the PEI-coated Fe₃O₄ NPs.